Authorities are investigating a fire that ignited inside an official ballot drop box outside the Baldwin Park Library on Sunday night.

Crews responded to 4181 Baldwin Park Blvd. at around 8 p.m. to find the fire, the Los Angeles County Fire Department said.

Baldwin Park police also responded to the scene and said the fire was inside the secured ballot box.

Arson investigators are handling the probe, according to police. Officials have not announced any arrests.

Staff last picked up ballots from the site at 10:10 a.m. Saturday, Oct. 17, the L.A. County Registrar’s Office said Monday. The department encouraged those who dropped off their ballot after that time to call 562-503-2445 or email vbmdropoff@rrcc.lacounty.gov.

Other voters who used the drop box can also call the registrar to verify that their ballot was received.

The Registrar’s Office said it has reported the incident to the FBI and attorney general. Election officials have also requested any available footage to learn what caused the blaze and are working to notify any voters whose ballots may have been affected.

Meanwhile, the damaged drop box has been closed and staff is “immediately” increasing the frequency of pickups at all other official drop box locations.

“The arson of an official ballot drop box by the Baldwin Park Library in the First District has all the signs of an attempt to disenfranchise voters and call into question the security of our elections,” said L.A. County Supervisor Hilda Solis in a statement. “Tampering, or attempts to tamper, with our democracy will not be tolerated.”

All registered voters in California should automatically get a mail ballot that could be mailed back or returned to an official ballot drop box or polling location by Nov. 3. (The “traditional” deadline to register is Monday, Oct. 19. But those who miss it can still vote. Click here for more information.)

Voters can sign up to receive call, text or email alerts about the status of their ballots on california.ballottrax.net/voter.